The present invention relates to resonators and has particular relation to quartz resonator gyros [1]. Pairs of such resonators are particularly useful in making small resonator gyros in which one resonator is electrically driven at a given frequency and a second resonator is mechanically driven by the first and by any rotation the second resonator is undergoing. The second resonator produces an electrical signal which can be compared with the signal driving the first resonator. The rotation can be deduced from this comparison.
FIG. 1 shows the prior art. A resonator 10 is comprised of a tuning fork 12 etched from a single crystal of quartz, supported by a base 14. Single crystal quartz is a piezoelectric material. Leads are applied to the electrodes, 18 and 16, placed on the sides and top-bottom of the tuning fork 12 respectively. The electrodes 18 and 16 are selected such that the application of an oscillating voltage to the electrodes 18 and 16 will cause the tuning fork 12 to oscillate inward and outward at the same frequency. An inverted resonator (not shown) may conveniently be placed on the underside of the base 14 and be driven by the above described resonator 10. The resonator 10 may also be used in any other application wherein electrical oscillations are to be converted to mechanical oscillations, or vice versa. A resonator of this type will generally oscillate only at a very sharply defined resonant frequency, which is often a very desirable characteristic.
FIG. 1 shows the resonator 10 in its erect position, ready for use. It is fabricated, however, in a recumbent position. A large horizontal sheet of single crystal quartz is etched into a large number or resonators. The side of the resonator upon which electrode 16 is placed is therefore the upper surface of the resonator, while the side opposite the upper surface is the lower surface. The resonator is designed to resonate inward and outward. The side of the resonator upon which electrode 18 is placed is therefore an outer surface, while the side upon which the unnumbered electrode parallel to electrode 18 is an inner surface. The side of each tine opposite an outer surface is an inner surface, and vice versa.
The prior art has a number of drawbacks. Single crystal quartz is difficult to produce and it is difficult to chemically etch. The tuning fork is generally formed from the crystal by lithography followed by long (about 20 hours) chemical etching times in caustic liquids. Anisotropic etching results in rough morphology, low yield, and low reproducibility. The entire process is expensive. The electroding process for the current devices requires electrodes on faces and walls of each tine to suppress vibrational mode crosstalk. This crosstalk to undesired modes, is introduced because the piezoelectric tensor matrix of single crystal quartz is not symmetric.
Applicants avoid the limitations of the prior art by forming the tuning fork from a non-piezoelectric material rather than from single crystal quartz. Examples of such materials are fused quartz, silicon, GaAs, or CVD diamond. Some piezoceramics are well known to have piezo coefficients (piezoelectric strain constants) 100 to 250 times that of single crystal quartz. Only a thin fill of piezoceramic, many orders of magnitude thinner than the tines of the tuning fork itself, is required to be deposited on the top and/or bottom side of the tuning fork. Because of the thin film nature of the piezo films, and the non-piezo nature of the bulk resonator substrate used in the present invention, undesired mode coupling is eliminated, and no electrodes are needed on the side walls of the tuning fork tines, as is the case in the prior art. Separation of the mechanical and piezo functions of the resonator gyros allows flexibility of optimization of each function separately and improves the device performance and low cost manufacturing.